1. Field of the Invention
The present invention relates to a fluid bearing for supporting a part rotatably or linearly movably in a non-contact manner.
2. Description of Related Art
In an air bearing as one of static-pressure fluid bearings, pressurized air is fed into a gap of several μm between bearing surfaces from air spout holes. It is known that bearing concaves in the form of grooves or dimples having depth of several μm formed around the air spout holes improve a bearing rigidity by several times. If depths of the bearing concaves are too small, the bearing rigidity is lowered and if the depths of the bearing concaves are too large, a flow rate of the fluid is increased, tending to cause minute vibrations. Thus, the precision of depths of the bearing concaves gives great influences on performance of the air bearing, and thus high precision in forming the bearing concaves is required.
As a method of forming bearing concaves for the fluid bearing, machining for removal such as grinding and cutting have been adopted. Further, it has been adopted to form bearing concaves having predetermined widths, depths and lengths by irradiating a laser beam.
JP 10-113832A discloses a method of manufacturing a dynamic-pressure fluid bearing in which pressure is generated by flow of fluid caused by rotation of a shaft. Dynamic-pressure generating grooves are formed by moving a cutting tool having groove cutting blades at outer periphery thereof in a through hole provided in a bearing member while rotating the cutting tool relative to the bearing member. Various dynamic-pressure generating grooves are formed by varying a rotational speed of the cutting tool, a shape of the blades and the number of blades of the cutting tool.
In JP 2001-159426A, it is described to form dynamic-pressure generating grooves on at least one of bearing surfaces by cutting so as to keep a distance between the bearing surfaces of the dynamic-pressure fluid bearing and also generate a dynamic pressure. This document discloses forming coating on a bearing surface and irradiating a high energy beam such as a laser beam on the coating to form dynamic-pressure generating grooves having predetermined widths, depths and lengths.
The method of forming bearing grooves of the fluid bearing by cutting causes protrusions at outer peripheries of the formed grooves and thus it is required to remove the protrusions, so that a manufacturing cost is increased. Further, depths of the grooves are set in the order of 1 μm and it is required to form the bearing grooves with high precision in size and position, and thus it is difficult to form such bearing grooves by machining. Further, the method of forming the bearing grooves by irradiating the high energy beam such as the laser beam on the coating layer necessitates a laser machining apparatus to increase a manufacturing cost.